The spin and orbit of the newly discovered pulsar IGR J17480-2446

TL;DR

This paper analyzes the spin and orbital characteristics of the newly discovered accreting pulsar IGR J17480-2446, providing insights into its binary system, magnetic field, and its classification among recycled pulsars.

Contribution

It offers the first detailed measurement of the pulsar's orbital parameters, spin-up rate, and magnetic field estimates, revealing its nature as a slow, mildly recycled accreting pulsar.

Findings

Binary system with a 21.27 hr period and companion >0.4 Msun.

Pulsar spin-up rate between 1.2 and 1.7E-12 Hz/s.

Magnetic field estimated between ~2E8 G and ~2.4E10 G.

Abstract

We present an analysis of the spin and orbital properties of the newly discovered accreting pulsar IGR J17480-2446, located in the globular cluster Terzan 5. Considering the pulses detected by the Rossi X-ray Timing Explorer at a period of 90.539645(2) ms, we derive a solution for the 21.27454(8) hr binary system. The binary mass function is estimated to be 0.021275(5) Msun, indicating a companion star with a mass larger than 0.4 Msun. The X-ray pulsar spins up while accreting at a rate of between 1.2 and 1.7E-12 Hz/s, in agreement with the accretion of disc matter angular momentum given the observed luminosity. We also report the detection of pulsations at the spin period of the source during a Swift observation performed ~2 d before the beginning of the RXTE coverage. Assuming that the inner disc radius lies in between the neutron star radius and the corotation radius while the source shows pulsations, we estimate the magnetic field of the neutron star to be within ~2E8 G and ~2.4E10 G. From this estimate, the value of the spin period and of the observed spin-up rate, we associate this source with the still poorly sampled population of slow, mildly recycled, accreting pulsars.